Precision-measuring transducers having two relatively movable members, each member being spaced from the other and having electrically coupling patterns positioned on the facing surfaces thereof are well known in the art. In their operation, at least one of the patterns on one of the members is electrically energized, and an output signal is detected on at least one of the patterns on the other member to give an indication of the relative position of the two members.
Transducers of this type are manufactured under the trademark INDUCTOSYN.RTM. by Farrand Industries, Inc., and the electrical coupling between the circuit patterns on the surface of the members can be of the electromagnetic type as described in U.S. Pat. No. 2,799,835, or of the electrostatic type as described in U.S. Pat. No. 3,961,318. The relative motion between the transducers can be either linear or rotary. The present invention, however, is limited to transducers for the precision measurement of linear dimensions.
The electrically coupling conductive patterns on the surface of the transducer elements, as described in the aforementioned patents, have pluralities of portions with precisely uniform pitch and length. Slight deviations from or variations of pitch or length produce noticeable effects on the accuracy and precision of the transducers involved.
Typically, one of the transducer members, called a "scale" member, can be provided with a rectangular periodic wave pattern of substantially uniform pitch; and the other transducer member, called a "slider" can be provided with two separate rectangular periodic wave patterns ("sine and cosine" windings), the two patterns being arranged in space quadrature, i.e. one of the two patterns is spaced relatively to the other by N+.lambda./4 where N is an integer and .lambda. is the wavelength of the two periodic slider patterns. In electrical operation of the transducer, the two members, scale and slider, are positioned with an air gap between them, the scale and slider patterns being electrically coupled, so that when the scale pattern is energized by an alternating current voltage, two separate sine and cosine voltages appear across the two slider windings respectively, indicative of the relative linear position of the scale and slider expressed in degrees of a circle, where 360.degree. represents one wavelength of the transducer pattern. Alternatively, the sine and cosine windings of the slider member can be appropriately excited to determine a particular relative position between the scale and slider patterns, and an electrical signal will accordingly be induced across the scale winding, the amplitude of which is indicative of the difference between that determined position and the actual relative position of scale and slider members.
In general, the transducer electrical patterns are made by a photofabrication process. This involves a number of steps including:
(1) making the photographic mask of the pattern on glass; PA1 (2) bonding a conductive metallic sheet on a base material; PA1 (3) sensitizing the conducting sheet with a photoresist material; PA1 (4) exposing the photoresist with the photographic negative; PA1 (5) developing the photoresist; and PA1 (6) etching the metallic sheet material.
Each of these processes can introduce errors, particularly errors of length or of pattern pitch.
It is a function of the present invention to adjust for such variations in pattern length which may be present in these electrical patterns by mechanically varying slightly the dimension of the substrate member on which they are affixed so as to improve the resulting accuracy of the transducer.